Solid-supported Liquid Membrane Research Articles

Solvent Extraction of Gold(III) by 2-Ethylhexanol and Modeling of Facilitated Transport across a Supported Liquid Membrane

The solvent extraction of gold(III) by undiluted 2-ethylhexanol or dissolved in toluene from a HCl solution has been investigated in this paper. The numerical analysis of gold distribution data suggests the formation of HAuCl4·L and HAuCl4·2L (L = 2-ethylhexanol) species in the organic phase, with formation constants K11 = 38 and K12 = 309, respectively. The results derived from gold(III) distribution have been implemented in a solid-supported liquid membrane system. The influence of several variables on gold transport has been considered: feed and receiving phases’ stirring speeds, HCl and gold concentrations in the feed phase, and carrier concentration in the membrane phase as well as the presence of base metals (Fe, Cu, Ni) and platinum-group metals (PGMs) in the feed phase. Gold transport is influenced by the stirring speed of the feed phase and the variation in HCl and gold (feed phase) and carrier (membrane phase) concentrations. Also, diffusional resistances to mass transfer are estimated, and the contribution of each resistance to gold transport is estimated. Gold is recovered as zero-valent nanoparticles.

Electrochemical Characterization of Solid-Supported Liquid Membrane Systems Based on Aryl Aldoxime, 2-hydroxy-5-nonylbenzaldoxime Ionophore

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Solvent Extraction of Au(III) by the Chloride Salt of the Amine Alamine 304 and Its Application to a Solid Supported Liquid Membrane System

The extraction of Au(III) by the chloride salt of the amine Alamine 304 (R3NH+Cl−) in xylene from hydrochloric acid solutions has been investigated. The analysis of metal distribution data by numerical calculations suggested the formation of the species R3NH+AuCl4 − in the organic phase with formation constant log K ext = 5.44. The results obtained on Au(III) distribution have been implemented in a solid‐supported liquid membrane system, where in NaSCN solutions were found to be the most effective to strip the metal from the organic solution. Influence of membrane composition, metal concentration on gold transport, and the selectivity of the system have also been studied.

Facilitated transport and preconcentration of the herbicide glyphosate and its metabolite AMPA through a solid supported liquid-membrane

A solid supported liquid-membrane (SLM) system for the transport and preconcentration of the herbicide glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) has been designed and characterised. The influence of the chemical composition of the system as well as membrane configuration on the transport properties were investigated. The best extraction conditions were achieved by adjusting the pH of the aqueous feed phase to 12 (0.1 M NaOH). Among the different options tested, a 0.1 M HCl solution was found to be the most effective to strip glyphosate and AMPA from the loaded organic phase. The effect of carrier concentration and the nature of the organic solvent were also tested and the best results were obtained when working with 0.2 M Aliquat 336 in dodecane modified with 4% dodecanol. Under these chemical conditions some preconcentration experiments were run using two different geometries of the membrane: a hollow fiber liquid-membrane (HFSLM) and a laminar membrane system (LSLM) where the stripping solution can be recirculated. The best results were obtained for the liquid-membrane system in HF configuration, with concentration factors of 19 and 2.5 for glyphosate and AMPA, respectively.

Iron(III) transport using a supported liquid membrane containing Cyanex 921

A study of iron(III) transport through a solid-supported liquid membrane using the phosphine oxide Cyanex 921 as carrier has been carried out using batch experiments. A model is reported describing the transport mechanism which consists of a diffusion process through a source aqueous diffusion layer, a fast interfacial chemical reaction and diffusion of HFeCl 4·L 2 (L, the extractant) through the membrane. The transport system is studied as a function of several variables, such as the diluent of the organic phase, metal concentration in the source phase, etc., along with the composition of the receiving solution. The mass transfer coefficient was calculated from the model as 23 μm/s and the thickness of the source aqueous boundary layer was calculated to be 44 μm. The behaviour of Cyanex 921 has been studied with respect to other organophosphorus extractants and also the selectivity of the membrane-carrier system on various metal-bearing aqueous solutions.

Modelling of mass transfer in facilitated supported liquid membrane transport of gold(III) using phospholene derivatives as carriers

An experimental study of gold(III) transport through solid-supported liquid membranes using phospholene derivatives as carriers has been performed using batch experiments. A model is reported describing the transport mechanism which consists of a diffusion process through a feed aqueous diffusion layer, a fast interfacial chemical reaction and a diffusion of HAuCl 4L and HAuCl 4L 2 through the membrane. The mathematical equations describing the rate of transport are derived and correlate the membrane permeability coefficient to diffusional and equilibrium parameters as well as the chemical composition of the system, such as extractant concentration in the membrane phase and HCl concentration in the feed phase. The experimental data are explained with the derived equations, and the diffusion resistances to mass transfer are evaluated. The influence in the transport of stirring speed in the feed phase, the nature of the diluent and stripping agent, and the type of polymeric support have been also discussed.

Chemical pumping of rhodium by a supported liquid membrane containing Aliquat 336 as carrier

The mass transfer of Rh(III) from aqueous feed chloride solutions containing SCN − through a solid-supported liquid membrane (SSLM) consisting of Aliquat 336 dissolved in dodecane has been studied. The influence of hydrodynamic conditions as well as the chemical composition of the system on the permeation rate was investigated. Among the reagents tested as carriers, quaternary amines have been shown to be the most effective for the metal transport. Aliphatic organic diluents were chosen to avoid the degradation of the polymeric support, and 1-dodecanol was used as a modifier to increase the solubility of the extractant. The presence of thiocyanate in the feed solution was essential for the extraction of Rh(III). Furthermore, previous heating of the feed solution was necessary in order to form the extractable complex Rh(SCN) 6 3. Different reducing compounds were tested as stripping agents, and 1.0 M NaHSO 3 solution was found to be the most effective to strip Rh(III) from the organic phase. Under these conditions, transport of Rh(III) through the membrane against its concentration gradient was achieved. The transport behavior of palladium and platinum in the proposed liquid membrane system was also studied. The obtained results reveal the possibility of exploiting the kinetic differences in the chemistry of the platinum group metals in the design of a process for the separation of these three metals.

Facilitated Transport of Gold through a Membrane via Complexation to Thiourea-Based Reagents

Abstract The facilitated transport of Au(III) from hydrochloric acid solutions through double solid supported liquid membranes (SSLMs) is reported. The organic phase consisted of a chloroform solution of thiourea-based extraction reagents, dodecyl-thiourea (DTH) or nonylthiourea (NTH), physically absorbed onto microporous polypropylene films, Celgard 2500 or Celgard 2400 (Celanese Plastic Inc.). A cell composed of three compartments, including a reservoir of organic solution, with double SSLM was used in this study. Aqueous solutions of thiourea, KSCN, or Na2S2O3 were used for removing Au(III) from the membrane phase. The permeability coefficient, P, of the SSLM was determined from the slope of Iog[Au]/[Au]o or log A/Ao vs time plot. The influences of the stirring rate in aqueous feed and organic solutions, of the stripping reagents and their concentration, of the carrier concentration, and of the concentration of HCl in the aqueous feed on the permeability coefficient were determined. A model describing ...

Determination of chloride complex of Au(III) by capillary zone electrophoresis with direct UV detection

Capillary zone electroophoresis was used for the determination of gold(III) chloride using direct UV detection at 220 nm. By using a capillary column 70 cm long, the optimum applied voltage was found to be around −7 kV; carrier solution containing 0.1 M HCl and 0.4 M NaCl was used as an additive. At this pH, the electroosmotic flow-rate appears to be almost zero. The effects of chloride concentration and the applied voltage on determination efficiency are discussed. Heat generation appeared negligible as the electric current and migration time were reproducible. The analytical performance is discussed in terms of the detection limit, linearity and reproducibility. A single trial was performed in 18 min. Under these conditions, Pd(II) and Pt(IV) can also be determined; the order of mobility in the electropherogram was as follows: PdCl 4 2− > PtCl 6 2− > AuCl 4 −. The method was applied to the monitoring of Au concentration during a study of AuCl 4 − transport through solid-supported liquid membranes.

New sulphur-containing reagents as carriers for the separation of palladium by solid supported liquid membranes

N 2-substituted N 1-phenylbenzamidines and N′-disubstituted N-benzoyl thiourea derivatives, which contain donor S, N and O atoms, have been studied as carriers for the facilitated transport of Pd(II). These reagents have been shown to be effective in the solvent extraction of palladium. Thiocyanate ions or thiourea have been employed as stripping agents. The use of these reagents as carriers in liquid membranes was carried out by developing both bulk and supported liquid membranes. The presence of NaSCN in the feed solution at appropriate concentration results in an increase in the rate and mass transfer of palladium. N-benzoyl thiourea derivatives have been shown to be the most effective for Pd(II) transport and several compounds with enhanced lipophilic characteristics were prepared. A comparison of the results obtained reveals a significant influence of lipophilicity (side chain substituent) on the permeability of Pd(II).

Preconcentration of neptunium by supported liquid membranes for luminescent analysis of environmental samples

The possibilities of liquid membrane preconcentration of neptunium from environmental samples of different nature have been studied. The use the solid-supported liquid membrane containing a trioctylmethylammonium nitrate carrier allows to achieve preconcentration factors of 102–5×102. The teflon solid support does not interact with the luminescent matrix (CaF2, PbMoO4) during calcination at 900 °C, so it makes practical to measure the neptunium content by luminescence without reextraction to aqueous solution. As a result, the detection limit of neptunium is lowed down to 10−13 g ml−1 and 5×10−13 g g−1 for pure solutions and soils, respectively.

Two fibre-optic sensors with confined enzymes and coenzymes: development and application

A fibre-optic biosensor based on the fluorimetric detection of NAD(P)H consumed or generated during enzymatic reactions is described. The design combines a miniaturized fluorimeter with a low-volume membrane reactor and utilizes flow-injection analysis principles. Two types of membrane reactor were developed and tested. In the first version, enzymes and a macromolecular nicotinamide adenine dinucleotide coenzyme derivative of polythyleneglycol, PEG- N 6-(2-aminoethyl)-NAD(P)(H), are retained in the direct vicinity of the sensor tip. In the second version, a solid-supported liquid membrane was used to retain native coenzyme, while substrates and products were transported via selective carriers through an organic membrane barrier. The automated determination of phenylpyruvate, pyruvate, lactate, formate, ethanol and mannitol concentrations in model media was possible in the range of 50–1500 μmol l −1. The usefulness of the biosensor concept reported for real process monitoring in biotechnology or for medical purposes was demonstrated on different examples including the determination of ethanol for Saccharomyces cerevisiae cultivation.

Accelerated mass transfer of palladium(II) through a selective solid-supported liquid membrane containing Cyanex 471

Accelerated mass transfer of palladium(II) through a selective solid-supported liquid membrane containing Cyanex 471

Separation of Titanium and Iron in Brines by Solid Supported Liquid Membrane Using Tributylphosphate, TBP, As Carrier

Abstract Separations of titanium and iron in highly concentrated salt solutions containing tributylphosphate, TBP, have been accomplished by a solid supported liquid membrane. Different parameters affecting mass transfer of the metals have been studied. Based on the formation of metal chloro complexes conditions for the separation of Fe from Ti were determined. Also, a model for the facilitated transport through the liquid membrane has been proposed.

Accelerated mass transfer of palladium(II) through a selective solid-supported liquid membrane containing Cyanex 471

The mass transfer of Pd(II) from aqueous feed chloride solutions containing SCN − through a solid-supported liquid membrane (SSLM) consisting of Cyanex 471 dissolved in cumene was studied. The influence of hydrodynamic conditions and chemical composition of the system on the permeation rate, mainly the effect of feed aqueous SCN −, was investigated. Two different approaches were used to explain the behaviour of the membrane system. First, a 2 3 experimental factorial design showed a slight influence of the chemical parameters, especially SCN − and Pd(II) concentrations. Second, a diffusion model was applied to characterize the mass transfer of Pd(II); thus the diffusion coefficients of organic permeating species and the thickness of the aqueous diffusion layer were estimated. The proposed liquid membrane process was applied to the separation of palladium from platinum in a synthetic sample solution at concentrations similar to that obtained in the leaching of spent automotive catalysts. The results indicated that Pd(II) can be separated effectively from Pt(IV).

A Combination of Selective Mass Transport and Enzymatic Reaction: Enzyme Immobilization in Liquid Surfactant Membranes

AbstractThe liquid surfactant membrane technique for immobilization of enzymes in enzyme emulsions is described in this paper. This offers the combination of selective mass transport and specific enzymatic reaction. Several applications are presented to show the potential of this technique for integration of enzymatic reaction, purification, and product accumulation to one single process step. A strategy for membrane optimization is given and discussed. In addition information on the selective mass transport through liquid surfactant membranes (enzyme emulsions and solid supported liquid membranes) and on the reaction modeling are presented.

A Study of the Permeation of Gold(III) Through Cyanex471x Solid Supported Liquid Membranes (SSLM)

Abstract A solid supported liquid membrane for the selective removal of Au(III) from chloride solutions has been developed by using Triisobutiphosphine sulfide (Cyanex 471x) In cumene as organic carrier. The membrane system is shown to be effective between chloride solutions ([Cl−]= 1.0 M) containing traces of Au(III) and SCN− 0.1 M solutions. Different kinds of at membrane supports have been studied. The results, expressed in terms of membrane permeability, show significant differences between the different supports employed, the polypropylene supports, being the most efficient.

Americium removal from nitric acid waste streams

Separations research at the Rocky Flats Plant /RFP/ has found ways to significantly improve americium removal from nitric acid/7M/ waste streams generated by plutonium purification operations. Partial neutralization of the acid waste followed by solid supported liquid membranes /SLM/ are useful in transferring and concentrating americium from nitrate solutions. Specifically, DHDECMP /dihexyl-N, N-diethylcarbamoylmethylphosphonate/ supported on Accurel polypropylene hollow fibers assembled in modular form transfers >95% of the americium from high nitrate /6.9M/, low acid /0.1M/ feeds into 0.25M oxalic acid stripping solution. Maximum permeabilities were observed to be 0.001 cm sec−1, consistent with typical values for other systems. The feed:strip volume ratio shows an inverse relationship to the fraction of metal ion transferred. Cation exchangers may be used to concentrate americium from the strip solution. Furthermore, OOD/iB/CMPO /or CMPO/ /octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide/ has been tested in an extraction chromatography mode. Preliminary results show CMPO to be effective in removing americium if the feed is neutralized to 1.OM acidity and iron/III/ is complexed with 0.20M oxalic acid.

Facilitated transfer of cationic drugs across a lipoidal membrane by oleic acid and lauric acid

The transfer of four β-adrenoceptor blocking agents of different lipophilicity across an artificial lipid membrane was measured using the rotating diffusion cells (RDC). A facilitated transport mechanism was established when oleic acid and lauric acid were incorporated in the membrane, using an appropriate pH gradient. The diffusion of metoprolol, oxprenolol and to a lesser extent propranolol was enhanced by an ion-pair mechanism in the presence of the fatty acids. The transfer of atenolol, the most hydrophilic of the drugs under investigation, was not enhanced. The results are useful in understanding the way in which charged molecules may be transported across biological membranes by ion pair mechanisms and also for the development of solid supported liquid membranes in separation technology.

The Role of Feed Metal Concentration in the Coupled Transport of Zinc through a Bis-(2-ethylhexyl)phosphoric Acid Solid Supported Liquid Membrane from Aqueous Perchlorate Media

Abstract The coupled transport of Zn(II) macroconcentrations (up to 100 mmol/dm3) and H+ through a solid supported liquid membrane (SSLM) consisting of bis-(2-ethylhexyl)phosphoric acid (HDEHP) dissolved in the aliphatic kerosene Isopar-H has been investigated as a function of the hydrodynamic characteristics and chemical composition of the system. The results were analyzed in terms of a model considering the aqueous and organic diffusion as well as chemical reaction rates in order to explain the observed zinc transfer rates. The analysis showed the importance of the carrier saturation phenomenon taking place as the metal concentration is increased and the subsequent minimization of the role of chemical reaction kinetics.